A wide variety of medical devices are made from thermoplastic polymers. Medical devices must be manufactured with greater care than general consumer products especially when inserted into the body or brought into contact with a wound or lesion. In the area of treatment devices, such as catheters, manufacturers must take great care to assure that the devices perform with an extremely high degree of reliability. At the same time there is a need to develop materials and improve processing techniques to obtain improvements in desirable properties such as tensile strength, flexibility, puncture resistance, and softness. One area in which development has been especially intense focuses on balloons deployed on catheters which are utilized for dilatation, especially angioplasty, for stent placement, for urinary treatment, and the like.
In preparing high strength balloons for medical devices such as dilatation and stent placement catheters, a variety of polymer materials have been used.
Levy, U.S. Pat. No. 4,490,421, describes use of PET of high molecular weight (1.0 IV or higher). The patent notes that the IV may decrease during processing into balloons. Such a decrease is believed to be related to polymer degradation caused by extrusion temperature and the time the resin is held in the melt. Lower molecular weight PET has also proven useful for preparing high strength balloons. See for instance Noddin et al, U.S. Pat. No. 4,963,313; Saab, U.S. Pat. No. 5,264,260; Wang et al U.S. Pat. No. 5,348,538. PET is a polyester derived from an aromatic diacid and an aliphatic diol.
Aliphatic polyamide balloons are described in Pinchuk, U.S. Pat. No. 5,108,412.
Polyurethane block copolymer balloons are described in Gahara, U.S. Pat. No. 4,950,239, and Anderson et al, U.S. Pat. No. 5,500,180. The polyurethane polymers may be derived from aromatic polyisocyanates.
Polyamide block copolymer balloons and polyester block copolymer balloons are described in Wang et al, U.S. Pat. No. 5,563,383. The polyamide block copolymers are entirely aliphatic, whereas the polyester block copolymers comprise aromatic poloyester segments and aliphatic polyether segments.
Various other polymers have also been used for catheter balloons.
A wide variety of polymer blends have also been described for such balloons, for instance, Sahatjian et al, U.S. Pat. No. 5,500,180; Chen et al, U.S. Pat. No. 5,554,120, Hamilton et al, U.S. Pat. No. 5,797,877. Some such blends have included compatibility enhancing additives. However, heretofore it has not been proposed to include additives which maintain or increase molecular weight during melt processing.
U.S. Pat. No. 5,328,468 describes balloons for a vascular dilatation catheter which is formed from an aromatic polyamide or alloy thereof.
U.S. Pat. No. 5,951,941 describes catheter balloons made from a block copolymer thermoplastic elastomer which may be a polyamide/polyether/polyester. The polyamide segments optionally may be aromatic polyamide segments.
U.S. Pat. No. 5,531,719 describes a catheter tube structure in which a proximal portion of the tube has an inner tube bonded to an outer tube. The inner tube maybe formed of a variety of materials including a polyamide elastomer block copolymer in which the polyamide blocks are optionally aromatic polyamide.
U.S. Pat. No. 6,033,778 describes an aromatic polyamide bristle said to be useful for tension member, fishing line and catheter.
Balloon catheters and other medical devices made from polymeric materials are most conventionally sterilized by exposure to a sterilizing gas such as ethylene oxide. High energy radiation (e-beam, x-ray and/or γ-ray radiation) has been used for sterilization of devices made from some polymers but is not widely suitable for devices made from thermoplastic polymers because it degrades many such polymers by inducing polymer scission, crosslinking and/or oxidization reactions. Aliphatic polymers are particularly susceptible to degradation from high energy radiation. Aromatic polymers have been observed to have resistance to high energy radiation.